The invention relates generally to rotor wheels supporting rows of blades or buckets for use in turbomachines. More particularly, the invention relates to rotating blades or buckets provided with part-span shrouds between airfoil portions of adjacent blades.
The fluid flow path of a turbomachine such as a steam or gas turbine is generally formed by a stationary casing and a rotor. In this configuration, a number of stationary vanes are attached to the casing in a circumferential array, extending radially inward into the flow path. Similarly, a number of rotating blades or buckets are attached to the rotor in a circumferential array extending radially outward into the flow path. The stationary vanes and rotating blades or buckets are arranged in alternating rows so that a row of vanes and the immediate downstream row of blades or buckets form a “stage”. The vanes serve to direct the flow path working fluid so that it enters the downstream row of blades or buckets at the correct angle. The airfoil portions (or, simply, airfoils) of the blades or buckets extract energy from the working fluid, thereby developing the power necessary to drive the rotor and an attached load, e.g., a generator.
The blades or buckets of the turbomachine may be subject to vibration and axial torsion as they rotate at high speeds. To address these issues, the blades or buckets in some stages may include part-span shrouds disposed on the airfoil at an intermediate radial distance between the tip and the root sections of the airfoil. The part-span shrouds are typically affixed to each of the pressure (concave) and suction (convex) sides of each airfoil, such that the part-span shrouds on adjacent blades matingly engage and frictionally slide along mated “hard faces” during rotation of the rotor.
In addition to part-span shrouds, it is often the practice to utilize tip shrouds attached to (or formed on) the radially outermost ends of the blade airfoils. Tip shrouds are also used to dampen vibrations and to control the amount of flexure at the outer tips of the blades or buckets.
There remains a need, however for bucket shroud designs that enhance bucket performance and/or that provide the opportunity to permit airfoil designs that also enhance performance by, for example, improving mechanical damping and creep life.